氡子核鉛-212在氧氣中的粒徑變化與聚合反應

　　　　　氧子核鉛-212微粒在氧氣環境下的活度粒徑大小分布，呈雙峰的分布，一在分子團區，另一在聚合區，分隔點約為2.5nm附近。此分子團區和聚合區微粒的分隔點，剛好落在微粒計數器（TSI 3025型）度量的低限值2.7nm附近。所以微粒計數器量到的微粒濃度，大致反應出聚合區微粒的個數濃度。微粒計數器量得的濃度越大，則由擴散分析器所分析得之聚合區活度比率也越大。對活度粒徑大小分布的影響，水分子因俱中和崩解聚合區微粒的能力，濕度越大發現聚合區微粒的可能越小，微粒計數器度量到的微粒濃度也越小。而在濕度介於10.3和11.0%，相近濕度的條件下，發現流經實驗腔的總流量率漸減少，則形成之聚合區氡子核微粒越多。實驗腔的總流量率越少將使得鉛-212滯留在實驗腔的時間越久，也使得其更有機會和其它微粒相遇、連結，進而聚合成較大粒徑的微粒。
　　　　　The activity size distributions of @Pb nenometer particles in oxygen gas have been measured by the diffusion battery. The distribution shows bimodel peaks associated with molecular clusters and coagulation particles. The particle size to distinguish the molecular clusters and coagulation particles is about 2.5 nm. Since the ultrafine condensation particle counter (UCPC, model 3025) has a lower detection limit about 2.7 nm, clusters in the molecular mode cannot be measured by the UCPC. Therefore, the greater the UCPC number concentration the larger is the fraction of particles in the coagulation mode. Further, larger water vapor suggests more electron scavengers to produce larger neutralization rates. This neutralization makes thoron progeny clusters to have smaller size. Thus, higher humidity leads to smaller cluster size and less UCPC number concentration. Keeping the humidity between 10.3% and 11.0%, the fraction of particles in the coagulation mode increased with decreasing total flow rate through the chamber. The lower total flow rate corresponds to the longer mean residence time of thoron progeny in the sampling chamber. Consequently, thoron progeny have better chance to collide, combine, and grow to a larger size.